The Age of Pterygophora californica 



T. C. Frye 

 University of Washington, Seattle 



The growth rings of Pterygophora californica have been known for 

 70 years. Ruprecht (IS^S) first called attention to them. Areschoug 

 (1884) calls attention to the fact that they are not easily counted since 

 some of them are often faint. MacMillan (1902) has gone rather fully 

 into their structure. Setchell (1912) refers to similar rings in Laminaria 

 as "annual(?)" rings; but whether each ring represents an annual growth 

 or not has not been settled. The question becomes the more interesting 

 when one considers that the work of Sauvageau (1915-1917) and of Kylin 

 (1916) seems to indicate that at least in some of the Laminariaceae the 

 conspicuous plant body is a sporophyte generation and therefore homo- 

 logous with the sporophyte of the pteridophytes and spermatophytes. 



Pterygophora californica is one of the Puget Sound algae showing the 

 rings about as clearly as any in the region. Thus, with a view to deter- 

 mining their significance, material was gathered at Blakeley Island and 

 at Cape Flattery, both in Washington. Since MacMillan (1902) has 

 already pointed out that the rings are partly due to different material 

 and partly to cell form, the structure of the rings does not form a part 

 of this paper, except that a section of a ring in a haptere is shown 

 (Fig. 5). 



So far as the writer has been able to find there is no literature on 

 the age of perennial algae. If the rings of Pterygophora are annual 

 growth-rings similar to those of trees, we have a means of estimating the 

 age of the plants fairly accurately ; but the method would help only in a 

 few genera of kelps. 



Winter plants of Pterygophora in Washington are mostly bladeless 

 stalks, even the terminal blade dying back to near its base. Occasionally, 

 however, leaves persist thru the winter. The summer plants are again 

 leafy. Thus the number of leaves present in the fall indicates roughly 

 the number grown that year. Sometimes blades are lost thru injury, but 

 their scars remain. Sometimes leaves persist throuout the winter, but 

 familiarity with the new ones in the early summer enables one to recog- 

 nize the old ones even in the fall of their second year. 



Each leaf when it disappears leaves a trace on the stalk (Fig. 9, 1). 

 On quite old stalks the basal traces are often obliterated, thus making it 



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